refactor: move bundled skills tree to repo root skills/

- Relocate runtime/skills -> skills/; runtime_skills_root() prefers oclaw/skills
  with fallback to legacy runtime/skills for unmigrated trees.
- session-bootstrap hook handler resolves repo root via PROJECT_ROOT.
- Update architecture/migration docs and in-tree skill references.

Co-authored-by: Cursor <cursoragent@cursor.com>

skills/tavily-search-pro/_meta.json

@@ -0,0 +1,11 @@
+{
+  "owner": "shaharsha",
+  "slug": "tavily-search-pro",
+  "displayName": "Tavily Search Pro",
+  "latest": {
+    "version": "1.0.0",
+    "publishedAt": 1770481308912,
+    "commit": "https://github.com/openclaw/skills/commit/7c907638c02746d4cdc5504cbe2816f52f6107ae"
+  },
+  "history": []
+}